The government filed notice on Thursday that it will seek the death penalty against accused Marathon bomber Dzhokhar Tsarnaev.

The government filed notice on Thursday that it will seek the death penalty against accused Boston Marathon bomber Dzhokhar Tsarnaev.

"The United States of America, by and through its undersigned counsel ... notifies the court and defendant Dzhokhar Tsarnaev that the United States believes the circumstances of the offenses charged ... are such that, in the event of a conviction, a sentence of death is justified," prosecutors wrote in their court filing.

Tsarnaev and his older brother Tamerlan are accused of setting off two bombs at the Boston Marathon finish line, killing three people and injuring more than 260 others. They are also accused of killing MIT Police Officer Sean Collier before becoming engaged in a shootout with police in Watertown days later. Tamerlan Tsarnaev died in the shootout.

Prosecutors outlined in the filing the reasons why a sentence of death for Tsarnaev, who was 18 at the time of the bombings, is justified.

"Dzhokhar Tsarnaev committed the offense in an especially heinous, cruel and depraved manner in that it involved serious physical abuse to the victim," prosecutors wrote.

Prosecutors said Tsarnaev "intentionally" killed and inflicted serious bodily injury on his victims and "specifically engaged in acts of violence, knowing that the acts created a grave risk of death to a person." They also highlighted his fleeing from the scene and "betrayal of the United States."

"Tsarnaev received asylum from the United States; obtained citizenship and enjoyed the freedoms of a United States citizen; and then betrayed his allegiance to the United States by killing and maiming people in the United States," prosecutors wrote.

What's more, prosecutors said his targeting of the Boston Marathon is an aggravating factor to consider.

"Tsarnaev targeted the Boston Marathon, an iconic event that draws large crowds of men, women and children to its final stretch, making it especially susceptible to the act and effects of terrorism," prosecutors wrote.

Shortly after the decision was announced, Celeste Corcoran, who lost both of her legs in the bombing, and her daughter Sydney, who was also injured, released a brief statement on their Facebook page.

"They have taken enough from us and many others and we trust in the U.S. legal system to do its job. Thank you for respecting our wishes to move on," the statement said.

Boston Mayor Marty Walsh, who as a state legislator voted against the death penalty, said on Thursday that he supports Holder's decision.

"We stand together as one Boston in the face of evil and hatred. Attorney General Holder has applied the law in this case, and I support the process that brought him to this decision," Walsh said.

US Attorney for the District of Massachusetts Carmen Ortiz said that she supports the decision and her trial team is prepared to argue for a sentence of death. However, she said she couldn't speak further about the decision.

"While I understand the public interest in this matter, we have rules that limit the release of information and the scope of public statements. The process by which this decision was made is confidential, and I will not comment further about that process other than to say that it entailed a careful and detailed consideration of the particular facts and circumstances of this case," Ortiz said in a statement.